U.S. Pat. No. 7,060,922 describes a push-button switch that includes a casing, a switch supported in the casing, a push button movably supported in the casing and an organic light-emitting diode (OLED) display device supported in the casing so that it remains stationary when the push button moves relative to the casing and which is visible through the transparent cover of the push button. The push button actuates the switch when it moves relative to the casing. The organic light-emitting diode (OLED) display device is arranged to display words and/or varying graphics.
EP-A-2053622 discloses a push-button switch with a display device that comprises a switch assembly including a casing that has an opening in the top thereof and a cover covering the casing, a switching element housed in the switch assembly and a plunger protruding upwards through a cover opening, wherein the plunger is guided in an ascending and descending movement inside the switch assembly to actuate the switch. A push button covering the switch assembly is mechanically connected to the plunger, and inside the push button there is an organic light-emitting diode (OLED) display device attached to a support plate. El display device is electrically connected to the switch assembly by means of a flexible ribbon connector.
JP-A-4002013 describes a push-button switch that comprises an optical sensing device to detect the state of the switch. The push-button switch comprises a base body and a push button that moves relative to the base body when it is depressed. The push button has an opaque portion intercepting the luminous trajectory between two elements of the optical sensing device when the push button is depressed.